Nautilus shows buttons with elements of your current path, e.g. if you are in /tmp/a/b, you will see three buttons that allows you to move quickly between directory structure: "tmp", "a", "b".

When you enter "b", then "a" and rename "b" to e.g. "x", button "b" remains the same, and obviously becames invalid because it points to non-existent path. I suggest to make mechanism that updates this button automatically, in the same way as bookmarks are updated after renaming the directory.

Other information: